For most of the last century, telephone communications were exclusively handled through circuit switched networks (generically identified as the public switched telephone network or “PSTN”). Circuit switching establishes a connection between a calling party and a called party. If all goes well, the circuit is maintained until the call terminates.
With the development of packet switching and the growth of the Internet, voice communication using packet switching technology has become an attractive alternative to the PSTN. Referred to as voice over Internet Protocol or “VoIP,” the technology to make packet-based voice services is evolving rapidly. Operators of subscriber access networks (SANs), including cable and fiber network operations, as well as local phone companies, Internet service providers (ISPs), and independent service companies (among others) are offering telephone services that can manage calls that originate and terminate on packet switched networks while also allowing VoIP calls to be terminated on, or initiated from, the PSTN.
FIG. 1 illustrates the logical elements of a SAN-based service. The SAN as illustrated utilizes a regional data center (RDC), RDC 1 128. Other regional data centers may be established by the operator of the cable network. The RDC 1 128 is connected to the managed IP network 115.
Managed IP network 115 is shown connected to a modem termination system (MTS) 120. A subscriber's modem 105 and multimedia (or media) terminal adapter (MTA) 110 connect to the MTS 120, which may be located at a headend (not illustrated). The MTA 110 handles voice compression, packetization, security, and call signaling to support a standard telephone 100 through an RJ-11 connector. An MTA 110 may be designed to be either a separate standalone device or to be embedded within modem 105. The MTA 110 and the modem 105 are each assigned both a media access control (MAC) and an IP address, even if integrated into a single device. The MTA 110 includes an interface to a physical voice device, e.g., a telephone. Additionally, the MTA includes a network interface, CODECs, and other circuitry necessary for processing telephony signals and IP packets. Logically, modem 105 is an “end-point” for high speed data service and MTA 110 is an end-point for digital telephone service. An end-point device is a network device that requires configuration and provisioning by the SAN in order to be permitted to communicate over the SAN. Other end-point devices include home gateway devices that provide connectivity between the SAN and home LANs and devices that provide video services to televisions and monitors.
As illustrated, cable modem (CM) 105, MTA 110, and MTS 120 are associated with RDC 1 128. Thus, RDC 1 128 is responsible for provisioning CM 105 and MTA 110. As part of this provisioning process, Dynamic Host Configuration Protocol (DHCP) server 140 provides DHCP services to modem 105 and MTA 110.
FIG. 1 also illustrates a number of logical components used to manage VoIP services over the cable network. RDC 1 128, which is associated with modem 105, MTA 110, and MTS 120 supports a softswitch 130 that manages and maintains a call state for VoIP services provided to telephone 100. While softswitch 130 is illustrated as residing within RDC 1 128, this is not meant as a function limitation. Softswitch 130 may be located outside RDC 1 128 and connected to it via a network segment such as a managed IP network 115.
MTA 110 is registered with softswitch 130. A telephone number assigned to a subscriber is associated at softswitch 130 with a fully qualified domain name (FQDN) of MTA 110.
A dynamic host configuration protocol (DHCP) server 140 provides functionality for provisioning or configuring MTAs and other communication devices for communication over the network. DHCP server 140 provisions MTA 110 with an IP address and an FQDN at boot up. The IP address and its associated FQDN for MTA 110 are stored in domain name server (DNS) 135 using dynamic DNS (DDNS). DNS 135 supports lookup requests from network devices based on either the IP address or the FQDN. By way of illustration and not as a limitation, a lookup request may be received by a softswitch 130, a network monitoring system (not illustrated), or by a provisioning system (not illustrated).
Using DDNS for MTA IP lookup in a large multi-system network exposes the VoIP service to the following limitations of current domain name look-up methodology. In a typical domain name look-up system, the DCHP server 140 dynamically updates DNS 135 with information relating the IP and FQDN assigned to MTA 110. However, if DNS 135 is unavailable for any reason, there is no assurance that an updated IP and FQDN for MTA 110 or modem 105 (or other end-point) will be stored in DNS 135. Additionally, in a DDNS system, the DHCP server 140 will queue the updated MTA 110 records for a fixed period of time. If the DNS 135 has not recovered before that fixed period of time has expired, the DHCP server 140 must “choose” to either cease issuing leases or the queue will be emptied. A request for the IP address of MTA 110 by softswitch 130 may then be fulfilled with the last record held by DNS 135. Consequently, a look-up is not always performed in real-time. Additionally, once DNS 135 loses synchronization, there is no way to resynchronize the data without rebooting all of the devices to obtain new leases.
Cable operators provide VoIP over a hybrid-fiber-coaxial (HFC) network in accordance with standards issued by CableLabs. The telephone call data is provided as packets over the high speed data path that also provides Internet connectivity. VoIP can also be provided over a fiber optic network.